Chemical process



Dec. 5, 1944. H. F. KOHLER 4 CHEMICAL PRocEss Filed Deo'.

III

wcm/maj normal parafn hydrocarbons.

Patented Dec. 5, 1944 CHEMICAL PROCESS Henry F. Kohler, Baytown, Tex., assigner to Standard Oil Development Company, a corporation of Delaware Application December 11,51941, Serial No. 422,490

'1s claims'. (o1. 26o-tsar) The present invention relates to improvements in the synthesis of hydrocarbons of relatively lower molecular weight to hydrocarbons of relatively higher molecular weight by alkylating an isoparafn with an olefin in the presence of concentratedsulfuric acid. More specifically, and in perhaps its preferred' and most useful modification, my invention relates to the alkylation of normally gaseous isoparains with normally gaseous olens to produce hydrocarbons boiling within the gasoline range.

Prior to my invention others had alkylated isoparafns With oleflns in a continuous process in the presence of concentrated sulfuric acid, that is to say, sulfuric acid having a concentration from 90 to- 98% by weight, to produce hydrocarbons boiling within' the gasoline range and having an improved octane rating. .I-Iowever, the prior processes of which l am aware are subject to numerous objections, since the alkylation of normally gaseous isoparafns with oleiins is a relatively recent development in the petroleum industry. l

The alkylati-on process is ordinarily carried out by mixing an olefin-containing stock with an isoparaiin-rich stock and charging the mixture to a reactor in which suitable conditions of ture leaving the reactor by suitable fractional I distillation. The olefin-containing stocks available usually contain considerable amounts of These normal paramns are undesirablefor several reasons, the

y stock to a reactor where suitable alkylation conmain objection being that the normal parains v must be separated' from excess i'soparafns by distillation, and hence large amounts of normal parains increase thenecessary distillation equipment and the resulting operating cost. Another objection is that the normal paraiins act as diluents in the alkylation reactor and reduce the concentration of the 'isoparaflim thereby impairing the quality of Athe alkylate. The normal parafns in the olen-containing feed stock can be substantially kept out of the alkylation reactor and product distillation equipment by using these-called two-'stage alkylation operation.I lny this process the olefin-containing stock is first charged to an absorber with concen` trated sulfuric acid where the olefns are abso'rbed` and the resulting acid-olefin extract sepditions are maintained. It is readily seen that vthe two-stage process has the advantage over the one-stage process in that the normal paraffins are removed in the first stage and therefore kept out of the alkylation reactor and product distillation equipment. As. concentrated sulfuric acid has a strong polymerizing and oxidizing action on the absorbed oleins, it is very important to use proper conditions inthe absorption stage, especially in regard to the molal acidolefin ratio. It has been found that when absorbing normal butylenes in the liquid phase in Sil-98% sulfuric acid considerable amounts oi' dialkyl sulfates are formed if the molal acid-oleiin ratio is 1:1 or lower. This is undesirable as part of the diallzyl sulfates will be carried out of the absorber in solution in the saturated hydrocarbons. This will involve an additional distillation to separate the dialkyl sulfates. lf slightly higher acid-oleiin ratios are used, say 1.5:1 or 2:1, considerable amounts of polymer will be formed, which is' also undesirable as the polymer is less valuable than the alkylated product obtained in the alkylation reactor.

My invention resides in the rst stage of the above indicated process. namely, in the absorption stage, for thereafter I proceed according to conventional methods. The gist of my invention resides in the concept of employing in the absorption stage of this two-stage alkylation process a large molal excess of sulfuric acid with respect to the olen content of the feed stock to the absorption zone s'o that, in accordance with the known law-of mass action, produce in the absorption zone a large preponderance of monoalkyl sulfate and a minimum amount of dialkyl sulfate. Furthermore, another advantage of using ailarge excess of concentrated sulfuric acid is to minimize the tendency of the olefin content of the charging stock to form. polymers. This is apparently contradictory to the earlier statement that the polymer formation increaseswhen the molal acid-olefin ratio increases :from

' 1:1 to 2:1. However, it was unexpectedly found that the feed stock to the absorption phase or zone should be substantially free of isooleiinv or tertiary oleiin, since it has been found' that these olens give very poor alkylation products.

' For example, suppose that isobutylene and norsorption zone, and consequently decrease the final yield of desirable alkylate to the extent that it is dissolved in the said liquefied normal parains withdrawn from the absorption tower.

The statementl made in the preceding paragraph, of course, applies generally to two-stage alkylation and is critical with respect to the present invention.

One object of the present invention is to carry out a two-stage alkylation process, that is to say, a process of alkylating isoprafiins, either normally gaseous or normally liquid, with, a normally gaseous or normally liquid olefin, in the first stage of which the olefin is absorbed in concentrated sulfuric acid having a strength of from 90 to 98%, and in the second, or alkylation, stage proper, to effect the alkylation of isoparaffin with the alkyl sulfates produced in the first stage. As stated before, the present invention resides in the concept, of employing in the first stage a large excess of sulfuric acid, namely, from 25 mols of sulfuric acid to 1 mol of olefin to 200 mols of sulfuric acid to 1 mol of olefin, and preferably I employ a ratio within the range of from 50 to 100 mols of sulfuric acid per mol of olefin. I also prefer to operate in the temperature range during the absorption stage of from to 75 F., depending on the olefin used, with a preferred absorption temperature range of from about to F.

My invention will-be best understood by reference to specific examples and, in order to aid in the understanding of the specific modiiication which Iam about to disclose, reference is made t0 the BCCOmDanying drawing which shows diagrammatically a fiow plan illustratinga preferred modification of carrying my invention into practical effect.

Referring in detail to the drawing, I represents the inlet tothe system of a liquefied olefin-containing feed stock containing 8 to 20% of normal olefin, such as normal butylene, the remainder being paraiiins and isoparaiiins, the isoolefln content being ireferably not more than 0.5% by weight for the reasons previously indicated. This charging stock is fed through cooler 2 into an elongated absorption tower 3 where it contacts sulfuric acid having a concentration of over 90% by weight, and preferably as high as 98% by weight, the said acid being discharged :into the absorption tower ythrough cooler 4 in line 5. Coolers 2 and 4 may be refrigerated by any suitable method and arev operated at such temperatures that the reactants in absorption tower 3 are maintained in the temperature range between 0 and 75 F., and preferably in the range from about 25 to 35 F. The acid introduced through line 5 into absorption zone 3 is pumped from alkylation product settler 6 wherein the sulfuric acid catalyst, the alkylation product, and unreacted hydrocarbons withdrawn from alkylation zone 1 through line 8 are settled and separated, the alkylation product and unreacted hydrocarbons being withdrawn through line 9 for separation and recovery by methods familiar to those skilled in the alkylation art.

f It is again pointed out that the novelty in my invention resides in the concept of so proportioning the molal ratio of acid to olefin in the feed stock that the said olefin is, as indicated, in the ratio of from 25 to 200 mols of acid per mol of olefin, with a preferred range of from 50 to 100 mols of acid per mol of olefin. I have found that when proceeding in this manner the major portion, if not all, of. the olefin reacts with the sulfuric acid in the absorption phase to form monoalkyl sulfate, .with minor amounts of dialkyl sulfate. This phase of my invention is important -because the dialkyl sulfate is relatively more soluble in the liquefied paraffin contained in the absorptionA zone than in the sulfuric acid, while the monoalkyl sulfate is relatively insoluble in the paraffin hydrocarbon. Therefore, when the liquefied paraffin is withdrawn from the absorption zone 3 by means of line I0, it contains a much less quantity of olefin in combined form, under conditions I have specifled hereinbefore, than in the procedure where substantially l mol of sulfuric acid is contacted in the absorption zone with 1 mol of olefin in the charging stock to the said absorption zone. The extract, comprising substantially all of the olefin charged to the absorption zone, in the form of monoalkyl sulfate is withdrawn from the absorption zone 3 through line I I and charged into alkylation reactor 1, together with an isoparaflin introduced into the system through line I2, as shown in the drawing. lThe alkylation is carried out in alkylation zone 1 under normal conditions of temperature, pressure, and time of contact and this alkylation stage, per se, does not form a part of my present invention.

As is well known to persons skilled in the alkylation art, it is extremely important that a high concentration of isoparaiiins should be maintained in the alkylation zone in order that maximum yields of highest quality product may be obtained. This fact is equally true in carrying out one of the objects of my invention. I attain this result by feeding enough isoparaffin through line I2 so as to maintain an isoparafiin mol percentage in the reactor hydrocarbon of at least 60%. I may also achieve a high isoparaflin-olefin ratio in the reactor zone by recycling acidhydrocarbon emulsion withdrawn from line 8 through line I3 and cooler I4 and reintroducing into the reaction zone through line I I. I

It is generally desirable to maintain a. volume ratio of about one part acid to one part of hydrocarbon in reactor l and, accordingly, the portion of acid-hydrocarbon emulsion entering settler 6 through line Il is in this ratio. Since the quantity of hydrocarbon in the system would be thrown out of balance if a greater quantity therecf were withdrawn through line 9 than is introduced as olefin in line I and as extraneous hydrocarbons through line I2, I maintain the desired balance between hydrocarbons withdrawn and acid fed to absorber 3 by recycling amajor portion of the settled hydrocarbons from settler 6 to reactor 1 through lines I1, I3 and II. This recycled hydrocarbon further assists in maintaining a high isoparafn concentration in the alkylation zone.

Since, during the alkylation reaction, the acid catalyst gradually becomes contaminated with complex organic materia! and water, it is generally desirable to discard through lin'e I5 ,a very small proportion of the acid flowing in line 5 and to replace this discarded acid by fresh. strong acid (preferably 98% by weight) through line I6 connecting with line Il. Only suiiicient acid is replaced in this manner so that the optimum strength is (maintained-in the alkylation zone.

In order to show the utility of my present inventon, the following three runs which I have made are set forth below. In these runs, isobutane was used as the isoparain, and the olefinic feed stock had the following composition by volume: 13.5% normal butylene, 0.1% isobutylene, 2.0% propane, 19.7% isobutane, and 59.7% normal butane.

lAcidole1ln mol ratio in absorber 119 49 24 Isobutane concentration in reactor hydrocarbon .mol per cent.. 81 82 76 Absorber temp` F 28 27 37 Reactor temg.. .F. 33 33 35 Acid strengt rcent '92.5 93.5 92.5 Time of contact in reactor A mriutes 118 106 90 Acid-hydrocarbon vol., ratio in reactor 0.79 0.89 1.13 Alkylate yield, wt. per cent of butylene 175 146 143 Aviation fraction in alkylaten. .vol. per cent.. 94 8 9' 72 Octane No. of aviation fraction. A. S. T. M. 95 94 94 Polymer. wt. per cent of butylene absorbed 3.8 4. 9 6. 9

In the foregoing examples it will be noted that when the acid to olefin ratio was 119 mols of acid to one of olefin in the feed stock, the total alkylate contained 94% of aviation fraction having f an A. S. T. M. octane number of 95, and the polymer formedwas only 3.8%. 0n the other hand, when the acid to olefin ratio was 49 mols of acid to one mol of olefin, the total alkylate contained 89% of aviation fraction having an octane number of 94; and the polymer was 4.9%. In the third run when the acid to olefin ratio was 24 to 1, the alkylated product contained only 72% of aviation alkylate having 94 octane number, and there was formed 6.9% of polymer. These data show that when a large excess of acid to olen was' employed inthe absorption zone, the yields of aviation fraction.` ywere larger, the octane number greater, and the amount of polymerformed was less.

Ithas beenshown from the foregoing specific examples that a denite improvement inthe twostage alkylation of -isoparafiins with oleiins may be secured by employing in the ilrst stage thereof a large excess of acid to olen. As heretofore explained when operating in this manner, the quantity of monoalkyl sulfate formed is greater, which means that the formation of dialkyl sulfate capable of dissolving'in the liqueed paran is less, so -that the over all yield from a given amount of olen and a given feed stock, is greater. It has also been shown by the data that 'the amount of undesirable polymers formed when proceeding in the manner indicated in the present invention, is substantiallyI less than that obtained when lower acid to olefin ratios are employed.

Although I have illustrated in the preceding specific examples the alkylation of isobutane with normal butyiene, it is to be distinctly understood that the same results may be secured with any normally gaseous or normally liquid isoparaln and/or normally gaseous or normally liquid normal olefin.

Many modifications of my invention, or falling within the spirit thereof, will suggest themselves to those familiar with this particular art.

\.What I claim is:

1. A process for the preparation of mono-alkyl sulfates suitable for subsequent alkylation with isoparains comprising vcontacting olens with concentrated sulfuric acid, the molal ratio of which is from 25-200 mols per mol of olefin.

2. A process for the preparation of mono-alkyl sulfates suitable for subsequent alkylation with. isoparains comprsingcontacting olens with concentrated sulfuric. acid, the molal ratio of which is from 50-100 mols per mol of olefin. 4

3. The process set forth in claim 1 in which the temperature is from 0-75F.

Li. 'Ihe process set forth in claim 2 in which the temperature is from 0-75 F.

5. The process set forth in claim l in which v the olens are in the liquid phase.

6. The process set forth ,in claim 2 in which the olens are in the liquid phase.

7. The process set forth in claim l in which.

the reaction between olefins and acid takes place in the substantial absence of iso-olonne.

8. The process set forth in. claim 2 in which the reaction between olefins and acid takes place in the substantial absence of iso-olens.

9. A process for the preparation oi. monobutyl sulfates suitable for the subsequent alkylation with isoparaflins comprising contacting normal butylene with concentrated sulfuric acid, the molal ratio of which is from 25-200 mols oi acid per mol of normal butylene. J

10. The process set forth. in cla 9 in which the olefins contacted with the sulfuric acid are ,in the liquid phase.

ll. The process set forth in claim 9 in which the ratio of acid to oleiin is from 50-100 mols of acid per mol of oleiln. v

12. The process set forth in claim 9 in which the temperature is between 0-'l5 il.

13. The process set forth in claim 9 in which the normal butylene is reacted with sulfuric acid in the substantial absence ci' isobutylene. 

